A number of prior art references have discussed the possibility of frying food products on a commercial scale using limited quantities of cooking oil. Basically, these disclosures can be classified into two broad groups. In the first group are those procedures which simulate frying by coating a food product with cooking oil prior to subjecting it to a separate convection heating step. In the second group are those patents which direct a pressurized spray of the oil directly against the food product.
Representative of the first group of prior art teachings is U.S. Pat. No. 4,269,861 to Caridis et al. According to this disclosure, french fried potatos are prepared for freezing and subsequent finish frying to closely resemble french fried potatos prepared directly from fresh potatos. The process includes the steps of peeling and trimming potatos, cutting them into strips, washing the strips, treating the washed strips with hot oil for a brief period, subjecting the strips to convection drying, again treating them with oil, and finally convection drying them to the desired final moisture content and a fat content of from about 3 to 7%. It is disclosed that in certain instances it may be desirable to omit immersing the strips in hot oil and that a substituted hot oil treatment can be employed. Specifically, it is disclosed that the strips may be passed through a curtain or spray of hot oil to achieve the desired oil pick-up on the potato product before subjecting the product to the hot atmosphere. Thus, while deep fat frying can be simulated by this process, it requires two distinct process steps: contact with hot oil in one step and contact with heated convection gases in another.
While this process does, to some extent, limit the quantity of oil picked up on the intermediate product, it is not disclosed as a process for preparing a completely cooked product. Moreover, the cooking steps set forth in the examples are disclosed to take about 9 minutes, to be followed by a subsequent deep fat frying step which takes another 2.5 minutes. Thus, much of the advantage of reduced oil pick-up which may be achieved during the preliminary processing would be lost where deep fat frying is necessitated for final preparation.
Representative of the second group of prior art teachings are British Pat. No. 621,821 to Crittall Kitchen Equipment Company, Ltd., et al, U.S. Pat. No. 4,134,998 to Liebermann, and U.S. Pat. No. 4,064,796 to Jones. According to the British patent, food articles are cooked by directing a pressurized spray of heated liquid cooking medium onto food articles that are supported in a cooking chamber, rather than by immersing them therein. While this procedure does somewhat decrease the amount of oil or other liquid heating medium which would be required for typical frying by immersion, a continuous spray would require substantial amounts of oil, and the pressurized spray of liquid which directly impinges upon the exterior surfaces of the food product would tend to dislodge delicate coatings of the type typically employed for chicken and the like. In addition, the continued impingement of the hot oil can cause a continuing disruption of the surface of the food, permitting the exudation of juices from the interior of the food. Moreover, the resulting product would be as saturated with fat as conventionally deep fat fried foods and would also necessitate the use of fats having high levels of saturated fatty acids to inhibit deterioration of the oil due to oxidation and exceeding its smoke point. Moreover, because all heat is supplied to the process by means of the hot oil, the ability for the oil to heat the food product is rapidly dissipated upon contact with the food and further heating is achieved only upon contacting the food with additional hot oil. Another disadvantage of the process is that the heating chamber is not sealed and steam generated during the heating process cannot be utilized to improve heating efficiency.
The disclosure of Liebermann is similar to that in the British patent in several regards, but differs principally in that the oil sprays operate at a more highly elevated pressure, disclosed as being between 10 and 70 psig. This higher pressure would have the disadvantage that it would even more readily tend to dislodge coatings and continue to disrupt the surface permitting exudation of food juices than would be expected according to the British patent disclosure. It is similar to that prior disclosure, however, with regard to the other disadvantages.
The disclosure of Jones is again similar to Liebermann and the British patent, but employs sprays from both the top and bottom of the food under conditions which provide a tranquil environment.
The use of convection heating is achieving a degree of acceptance for a number of cooking needs. According to the disclosure of U.S. Pat. No. 4,155,294 to Langhammer, cooking is achieved by directing a flow of hot air at food products held within a rotatable cage. However, because the cooking process is "greaselss", the cooking achieved cannot provide a true fried texture and flavor. Further examples of convection cookers are U.S. Pat. Nos. 4,011,805 to Vegh et al and 4,058,635 to Durth, both of which inject steam during convection heating. The food products cooked by these devices are even further removed than those of Langhammer from fried foods in terms of flavor and texture due to the steam cooking effects of the devices.
Accordingly, while the prior art has recognized that the amount of oil employed for a commercial frying process can be somewhat limited by impinging sprays of oil upon a food product, and that forced convection cooking is faster than oven baking, especially where steam is employed, there is no disclosure of a process or an apparatus which is capable of home use to achieve rapid hot oil heating of food products without the inefficiency, mess, cost, and dangers typically associated with frying foods. And, there remains a need for such a process and apparatus, especially one which could so improve efficiency, economy and simplicity of operation that consumers would not have to forgo the enjoyment of fried foods because of the limitations inherent in current home cooking methods. Moreover, it would be desirable to provide an improved cooking method and apparatus which could provide food products having the taste, texture and aroma of deep fat fried foods but use only a fraction of the normal amount of oil. This would be more attractive from a health standpoint due to lower amounts of residual fat within the cooked product and the ability to substitute highly polyunsaturated vegetable oils for the highly saturated fats which are currently required for practical and economic reasons.